The effectiveness of CO2 microsize bubbles for removal of Ca2+ ions in the leaching water discharged from the final landfill site was evaluated using imitation water. For the important parameter in the Ca2+ ion removal, it was found that the treatment in alkaline region above pH = 10 was optimum. The possibility of using CO2 microbubbles was examined by substitution of chemical Na2CO3, which is used in large quantities today. In addition, the excellence of CO2 microbubbles was demonstrated by comparing with CO2 millimeter size bubbles. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.